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Rise of the earliest tetrapods: an early Devonian origin from marine environment.

ABSTRACT: Tetrapod fossil tracks are known from the Middle Devonian (Eifelian at ca. 397 million years ago--MYA), and their earliest bony remains from the Upper Devonian (Frasnian at 375-385 MYA). Tetrapods are now generally considered to have colonized land during the Carboniferous (i.e., after 359 MYA), which is considered to be one of the major events in the history of life. Our analysis on tetrapod evolution was performed using molecular data consisting of 13 proteins from 17 species and different paleontological data. The analysis on the molecular data was performed with the program TreeSAAP and the results were analyzed to see if they had implications on the paleontological data collected. The results have shown that tetrapods evolved from marine environments during times of higher oxygen levels. The change in environmental conditions played a major role in their evolution. According to our analysis this evolution occurred at about 397-416 MYA during the Early Devonian unlike previously thought. This idea is supported by various environmental factors such as sea levels and oxygen rate, and biotic factors such as biodiversity of arthropods and coral reefs. The molecular data also strongly supports lungfish as tetrapod's closest living relative.

SUBMITTER: George D

PROVIDER: S-EPMC3136505 | biostudies-literature | 2011

REPOSITORIES: biostudies-literature

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Rise of the earliest tetrapods: an early Devonian origin from marine environment.

George David D Blieck Alain A

PloS one 20110714 7

Tetrapod fossil tracks are known from the Middle Devonian (Eifelian at ca. 397 million years ago--MYA), and their earliest bony remains from the Upper Devonian (Frasnian at 375-385 MYA). Tetrapods are now generally considered to have colonized land during the Carboniferous (i.e., after 359 MYA), which is considered to be one of the major events in the history of life. Our analysis on tetrapod evolution was performed using molecular data consisting of 13 proteins from 17 species and different pal ...[more]

PMID: 21779385

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Project description:The dichotomy of the earliest ecosystems into deltaic and floodplain forests was a long-standing view in paleobotany. The morphological traits such as nonbranching rootlets, bifurcating rhizomes, and bulbous bases of the primitive trees such as Eospermatopteris and lycopsids were considered adaptations to the lowland deltaic environments. In contrast, the traits of Archaeopteris trees such as wood, hierarchical branching networks of roots, and true leaves are an adaptation to the upland floodplain environments. The discovery of the Town of Cairo Highway Department (TCHD) fossil site in Upstate New York, where all major clades occupied a floodplain environment casts doubt on the validity of the environmental partition by the earliest trees at the higher taxonomic levels. This study aims to test the hypothesis of the environmental partition at the local scale by reconstructing the fossilized forest-floor landscape, the changes in the landscape over time, and the distribution patterns of the trees along the local environmental gradient at the TCHD site. To reconstruct the fossilized forest floor and to determine the environmental variations at the local scale, seven parallel cross-sections were drawn from south to north at THCH. The outcrop at the quarry floor measured 300 m in the north-south, and varied around 100-150 m in east-west direction. Primary sedimentary structures, the thickness of the sedimentary deposits that formed the forest floor and the surrounding quarry walls, paleosol features, and mega-fossils were measured, recorded, described, and mapped. Up to 3 meters deep drill-cores were extracted from the forest floor. The data was used to correlate the sedimentary deposits, and reconstruct the preserved landscape. Three dominant landscape features including an abandoned channel, an old-grown forest, and a local depression were recognized. These landscape features influenced greatly the pattern of local drainage, slope-gradients, patterns and durations of seasonal water pooling, paleosol developments, fossil distribution, and depositional environments. There is no evidence of environmental partitioning by trees at higher taxonomic levels at the local scale. The size and morphology of the root systems didn't determine the distribution of the trees along the local environmental gradient such as drainage patterns but played important roles in tree stabilization. Forests would go through self-thinning as they matured. Upon comparison, it was found that the forests in unstable environments showed greater resiliency compared to forests established in the stable environments.

Dataset Information

Rise of the earliest tetrapods: an early Devonian origin from marine environment.

Publications

Rise of the earliest tetrapods: an early Devonian origin from marine environment.

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